It is known that filled and unfilled compounded polymer materials, in particular polyethylene (PE) and copolymers thereof, can be produced by using organotin compounds or aromatic sulfonic acids (Borealis Ambicat®) as silanol condensation catalysts for the crosslinking of silane-grafted or silane-copolymerized polyethylenes. A disadvantage of the organotin compounds is their significant toxicity, while the sulfonic acids are notable for their pungent odor, which continues through all stages of the process into the final product. The compounded polymer materials crosslinked by sulfonic acids are generally not suitable for use in the food-and-drinks sector or in the drinking-water-supply sector, for example for production of drinking-water pipes, because of reaction byproducts. Dibutyltin dilaurate (DBTDL) and dioctyltin dilaurate (DOTL) are conventional tin-based silanol condensation catalysts, and act as catalyst by way of their coordination sphere.
It is known that moisture-crosslinkable polymers can be produced by grafting silanes onto polymer chains in the presence of free-radical generators, where moisture-crosslinking is carried out in the presence of the abovementioned silane hydrolysis catalysts and/or silanol condensation catalysts, after the shaping process. Moisture-crosslinking of polymers using hydrolyzable unsaturated silanes is practiced worldwide for the production of cables, pipes, foams, etc. Processes of this type are known as the sioplas process (DE 19 63 571 C3, DE 21 51 270 C3, U.S. Pat. No. 3,646,155) and the monosil process (DE 25 54 525 C3, U.S. Pat. No. 4,117,195). Whereas the monosil process adds the crosslinking catalyst before the first step of processing is complete, the sioplas process delays addition of the crosslinking catalyst to the subsequent step. Another possibility is to copolymerize vinyl-functional silanes together with the monomers and/or prepolymers directly to give the parent polymer, or to couple these subsequently by way of grafting onto the polymer chains.
EP 207 627 discloses further tin-containing catalyst systems and, with these, modified copolymers based on the reaction of dibutyltin oxide with ethylene-acrylic acid copolymers. JP 58013613 uses Sn(acetyl)2 as catalyst, and JP 05162237 teaches the use of carboxylates of tin, of zinc, or of cobalt together with hydrocarbon groups as silanol condensation catalysts, e.g. dioctyltin maleate, monobutyltin oxide, dimethyloxybutyltin, or dibutyltin diacetate. JP 3656545 uses zinc and aluminum soaps for crosslinking, examples being zinc octylate and aluminum laurate. JP 1042509 likewise discloses the use of organic tin compounds for the crosslinking of silanes, but also discloses alkyl titanic esters based on titanium chelate compounds. JP09-040713 discloses the production of silane-modified polyolefins by reacting a polyolefin and two modified silane compounds with use of an organic acid as silanol condensation catalyst.
It is an object of the present invention to develop novel silane hydrolysis catalysts and/or silanol condensation catalysts which do not have the abovementioned disadvantages of the known catalysts from the prior art, and which can preferably undergo a homogenization process or dispersion process with silane-grafted, and/or silane-copolymerized polymers, and/or monomers, or prepolymers. It is preferable that the silane hydrolysis catalysts and/or silanol condensation catalysts are waxy to solid, and/or have been applied to a carrier material.